Calcium is an essential mineral in the human diet for the preservation of human health. Calcium has been established as a key nutrient for skeletal rigidity; it is also known to impact metabolic, muscular, neurological, circulatory, and enzymatic processes. Calcium deficiency is a contributing cause of osteoporosis, a debilitating bone disease marked by a loss of bone mass.
Calcium is naturally found in many foods. The primary source of bioavailable calcium is milk and, more generally, dairy products. As people enter early adulthood, their consumption of dairy products tends to decrease. This may lead to a state of chronic calcium deficiency. This trend is particularly found with young women and could contribute to their high rates of osteoporosis development in later life. Additionally, many people are, or become, lactose intolerant as they age, thus reducing their ability to obtain natural, traditionally rich sources of this mineral.
Therefore, many alternate sources of food, drink, and supplements are currently being fortified with various organic and inorganic calcium salts. These alternate sources include pills, powders, food products, as well as a variety of fruit and non-fruit based juices and beverages. Many plaguing problems surround the provision of organoleptic qualities and bioavailability of these calcium-fortified sources. A common complaint with respect to fortified beverages is the relative insolubility of some of the added calcium salts, intolerable precipitation of solids, and a “chalky” feeling in the mouth upon drinking. Additionally, undesirable flavors and shelf instability contribute to a poor food product.
The fortification of various liquids with calcium, including orange, apple and other lo juices and beverages is an art currently practiced by juice and beverage manufacturers. Patents describing calcium fortification of fruit juices include several granted to Heckert and assigned to the Proctor and Gamble Company (for example, U.S. Pat. No. 4,722,847). These patents disclose calcium-citrate-malate (CCM) technology and teach that various calcium citrate and malate compounds, when combined in accordance with disclosed processing methods, will produce stable, fortified juices containing calcium levels at least equivalent to those normally occurring in milk (i.e., 350 mg/8 fl. oz).
U.S. Pat. No. 4,740,380 to Melachouris et al. discloses a calcium-fortified acidic beverage formulated using various calcium sources. U.S. Pat. No. 6,106,874 to Liebrecht et al. discloses a calcium-fortified nutritional beverage, which can be made from single strength juice. Calcium sources therein are natural milk mineral and Gluconal CAL® (manufactured by Glucona America).
Calcium fortification of grape-based beverages is especially challenging. The predominant organic acid in grape-based liquid (e.g. juice, wine, etc.) is, uniquely among fruit-derived liquids, tartaric acid. At pH levels above 2.8, tartaric acid will chemically dissociate into tartrate, bitartrate and hydrogen ions. As the pH of grape juice increases, the dissociation of tartaric acid becomes progressively more favored. Across the typical pH range of about 2.8 to about 3.9 for purple, red and white grape juices from Vitis labrusca, V. vinifera, and V. labrusca×V. vinifera hybrid grapes, the availability of tartrate ions for reaction with any added calcium to form insoluble crystalline calcium tartrate, is very high. Indeed, at relatively high pH and without the presence of calcium, potassium bitartrate crystals or “argol” in juice (or “wine stones” in wine) may be formed due to the naturally occurring concentration of potassium in grape-based product. This is commonly found in winemaking and the pertinent literature is abundant in addressing ways to solve this problem.
The formation of calcium tartrate crystals in grape-based liquids is known from past research on wines. This formation is dependent, for example, on the pH of the beverage, the storage temperature of the calcium plus beverage mixture, the presence of inhibitors, the ionic strength of solution, agitation of solution, and the length of time that the mixture is held in storage. Abgueguen and Boulton, (1993); McKinnon, 1993. Formation of calcium tartrate crystals may occur instantly upon the cooling of a pasteurized juice-calcium mixture, Alternatively, crystals may not occur for a substantial period of time. However, because calcium tartrate crystals have very low solubility in aqueous solutions such as grape juice, once formed, these crystals will tend to remain as an insoluble precipitate rendering the beverage organoleptically unacceptable with significantly diminished bioavailable calcium. After initial nucleation of these crystals, they will generally grow in size until the point of solution saturation is reached.